Biomedical subjects

Lucas M Bachmann

Publications and source records attributed to Lucas M Bachmann.

45 records · Page 3Linked to original sources

PubMed2003

Intraocular pressure measurements using dynamic contour tonometry after laser in situ keratomileusis.

PURPOSE: Thinning of the corneal stroma by laser in situ keratomileusis (LASIK) results in inaccurate low intraocular pressure (IOP) readings by Goldmann applanation tonometry (GAT). Dynamic contour tonometry (DCT) is a novel measuring technique, designed to measure IOP largely independent of corneal thickness and curvature. The purpose of this study was to compare IOP measurements using GAT and DCT in eyes undergoing LASIK for correction of myopia. METHODS: In a prospective, single-center study, central corneal thickness (CCT) and IOP were measured in patients undergoing first-time LASIK for myopia. IOP was measured before and after surgery using GAT and DCT. The untreated contralateral eyes served as paired controls. RESULTS: There was good concordance between the two tonometers in 62 normal eyes before LASIK. Corneal ablation of 90.0 +/- 49.18 micro m (median +/- SD) reduced IOP readings as measured by GAT by 3.0 +/- 1.9 mm Hg (P < 0.001). In contrast, no significant change in IOP readings was recorded by DCT (-0.2 mm Hg +/- 1.5 mm Hg, P = 0.30). There was no change in IOP in the untreated control eyes as measured by GAT and DCT. CONCLUSIONS: Significant decreases in IOP were recorded by GAT after LASIK for myopia. Measurements by DCT, however, did not reveal any significant changes in IOP.

Adult↗

PubMed2003

Prediction of intrauterine growth restriction with customised estimated fetal weight centiles.

OBJECTIVES: 1. To determine the value of third trimester customized estimated fetal weight centile ranking in the prediction of infants born with anthropometric features of intrauterine growth restriction (IUGR). 2. To compare the performance of customized centiles with fetal growth velocity in the prediction of IUGR. DESIGN: Prospective, observational study. SETTING: Department of Obstetric Ultrasound. POPULATION: Two hundred and seventy-four women with low risk pregnancies who were participants in a previously published longitudinal study of fetal biometry. METHODS: Third trimester estimated fetal weight customized centiles were obtained after adjustment for gestational age at the time of ultrasound, birth order and gender, maternal weight, height and ethnic origin. Fetal growth velocity was calculated using the increment in the fetal abdominal area over a mean 28-day interval. Fetal abdominal area growth velocity was expressed as a standard deviation (Z score). Three neonatal anthropometric measures were used to define IUGR: subscapular or triceps skinfold thickness <10th centile, ponderal index <25th centile, mid-arm circumference to occipito-frontal circumference <-1 SD. The ability of estimated fetal weight customized centiles <5th centile and <10th centile to identify growth restriction was determined by calculating likelihood ratios. MAIN OUTCOME MEASURE: Likelihood ratios for the prediction of neonatal anthropometric features of IUGR. RESULTS: Two hundred and fifty-eight infants had an estimated fetal weight customized centile calculated and one or more anthropometric measurements. The mean customized estimated fetal weight centile for cases with and without a low skinfold thickness were 16.4 vs 41.7 (P < 0.01); the mean values of customized estimated fetal weight centile for cases with and without ponderal index <25th centile were 22.8 vs 42.7 (P < 0.01); mean estimated fetal weight customized centiles for cases with and without mid-arm circumference to occipito-frontal circumference <-1 SD were 26.3 vs 40.5 (P > 0.05). A customized estimated fetal weight centile of 5 or less had likelihood ratios (95% CI) of 4.9 (2.7-6.3), 6.8 (4.5-10.6) and 6.3 (3.7-14) for skinfold thickness <10th centile, ponderal index <25th centile and mid-arm circumference to occipito-frontal circumference <-1 SD, respectively. An estimated fetal weight customized centile of 10 or less had likelihood ratios of 4.5 (2.6-8.6), 4.1 (2.5-7.2) and 7.1 (3.5-24) for skinfold thickness <10th centile, ponderal index <25th centile and mid-arm circumference to occipito-frontal circumference <-1 SD, respectively. In the prediction of a ponderal index <25th centile, the fetal abdominal area velocity likelihood ratio for a positive test is higher than the likelihood ratio for the 10th estimated fetal weight customized centile (P = 0.04) but is not significantly higher for the other outcomes. The fetal abdominal area velocity likelihood ratio is not significantly higher than the likelihood ratios for the fifth estimated fetal weight customized centile for any of the three outcomes. CONCLUSION: Customized estimated fetal weight centiles in the late third trimester are moderately useful in the identification of infants with IUGR but are less accurate than calculated growth velocity in the prediction of an infant with a low ponderal index.

Female↗

PubMed2003

Identifying diagnostic accuracy studies in EMBASE.

OBJECTIVE: The objective was to develop and test search strategies to identify diagnostic articles recorded on EMBASE. METHODS: Four general medical journals were hand searched for diagnostic accuracy studies published in 1999. Identified studies served as a gold standard. Candidate terms for search strategies were identified using a word-frequency analysis of their abstracts. According to the frequency of identified terms, searches were run for each term independently. Sensitivity, precision, and number needed to read (NNR) (1/precision) of every candidate term were calculated. Terms with the highest "sensitivity*precision" product were used as free-text terms and combined into a final strategy using the Boolean operator "OR." RESULTS: The most frequently occurring eight terms (sensitiv* or detect* or accura* or specific* or reliab* or positive or negative or diagnos*) produced a sensitivity of 100% (95% confidence interval [CI] 94.1 to 100%) and an NNR of 27 (95% CI 21.0 to 34.8). The combination of the two truncated terms sensitiv* or detect* gave a sensitivity of 73.8% (95% CI 60.9 to 84.2%) and an NNR of 5.7 (95% CI 4.4 to 7.6). CONCLUSIONS: The identified search terms offer the choice of either reasonably sensitive or precise search strategies for the detection of diagnostic accuracy studies in EMBASE. The terms are useful both for busy health care professionals who value precision and for reviewers who value sensitivity.

Databases, Bibliographic↗

PubMed2002

Accuracy of cervicovaginal fetal fibronectin test in predicting risk of spontaneous preterm birth: systematic review.

OBJECTIVE: To determine the accuracy with which a cervicovaginal fetal fibronectin test predicts spontaneous preterm birth in women with or without symptoms of preterm labour. DESIGN: Systematic quantitative review of studies of test accuracy. DATA SOURCES: Medline, Embase, PASCAL, Biosis, Cochrane Library, Medion, National Research Register, SCISEARCH, conference papers, manual searching of bibliographies of known primary and review articles, and contact with experts and manufacturer. STUDY SELECTION: Two reviewers independently selected and extracted data on study characteristics, quality, and accuracy. DATA EXTRACTION: Accuracy data were used to form 2x2 contingency tables with spontaneous preterm birth before 34 and 37 weeks' gestation and birth within 7-10 days of testing (for symptomatic pregnant women) as reference standards. Data were pooled to produce summary receiver operating characteristic curves and summary likelihood ratios for positive and negative test results. DATA SYNTHESIS: 64 primary articles were identified, consisting of 28 studies in asymptomatic women and 40 in symptomatic women, with a total of 26 876 women. Among asymptomatic women the best summary likelihood ratio for positive results was 4.01 (95% confidence interval 2.93 to 5.49) for predicting birth before 34 weeks' gestation, with corresponding summary likelihood ratio for negative results of 0.78 (0.72 to 0.84). Among symptomatic women the best summary likelihood ratio for positive results was 5.42 (4.36 to 6.74) for predicting birth within 7-10 days of testing, with corresponding ratio for negative results of 0.25 (0.20 to 0.31). CONCLUSION: Cervicovaginal fetal fibronectin test is most accurate in predicting spontaneous preterm birth within 7-10 days of testing among women with symptoms of threatened preterm birth before advanced cervical dilatation.

Biomarkers↗

PubMed2002

Systematic quantitative overviews of the literature to determine the value of diagnostic tests for predicting acute appendicitis: study protocol.

BACKGROUND: Suspected acute appendicitis is the most frequent cause for emergency operations in visceral surgery worldwide. In approximately twenty percent of all cases however, the diagnosis is incorrect and patients undergo surgery without having acute appendicitis. Operations of bland appendices put patients at risk and entail a serious waste of resources. Several highly accurate tests have been introduced to diagnose acute appendicitis. The false positive rate however, has not changed over the last twenty years. Given the variation that exists in both practice and research, the uncertainty regarding the quality of the underlying evidence, there is a clear need for comprehensive, systematic and quantitative overviews of the diagnostic value of the various tests purported to be predictive of acute appendicitis. METHODS: Literature will be identified searching general bibliographic databases (MEDLINE and EMBASE), specialist computer databases (DARE, Cochrane Database of Systematic Reviews, conference proceedings, MEDION, SCISEARCH, BIOSIS) without language restrictions. We will contact experts and the manufacturers of tests. Hand-searching will complete our searches. Identified articles will be selected according to populations, tests, outcomes and study design. Papers meeting the selection criteria will be appraised to rate their methodological quality. Analysis will include exploration of heterogeneity in results. We will conduct meta-analyses to generate summary estimates of test accuracy measures and summary ROC curves where appropriate. If meta-analysis is considered to be inappropriate, we will describe the identified evidence in the context of appraised quality. DISCUSSION: These reviews should lead to formulation of recommendations for current practice and future research.

Appendicitis↗

PubMed2002

Communicating accuracy of tests to general practitioners: a controlled study.

OBJECTIVE: To assess the extent to which different forms of summarising diagnostic test information influence general practitioners' ability to estimate disease probabilities. DESIGN: Controlled questionnaire study. SETTING: Three Swiss conferences in continuous medical education. PARTICIPANTS: 263 general practitioners. INTERVENTION: Questionnaire with multiple choice questions about terms of test accuracy and a clinical vignette with the results of a diagnostic test described in three different ways (test result only, test result plus test sensitivity and specificity, test result plus the positive likelihood ratio presented in plain language). MAIN OUTCOME MEASURES: Doctors' knowledge and application of terms of test accuracy and estimation of disease probability in the clinical vignette. RESULTS: The correct definitions for sensitivity and predictive value were chosen by 76% and 61% of the doctors respectively, but only 22% chose the correct answer for the post-test probability of a positive screening test. In the clinical vignette doctors given the test result only overestimated its diagnostic value (median attributed likelihood ratio (aLR)=9.0, against 2.54 reported in the literature). Providing the scan's sensitivity and specificity reduced the overestimation (median aLR=6.0) but to a lesser extent than simple wording of the likelihood ratio (median aLR=3.0). CONCLUSION: Most general practitioners recognised the correct definitions for sensitivity and positive predictive value but did not apply them correctly. Conveying test accuracy information in simple, non-technical language improved their ability to estimate disease probabilities accurately.

Aged↗

PubMedDate not supplied

To what extent can we trust home blood pressure measurement? A randomized, controlled trial.

Increasingly, patients measure and record their home blood pressure. However, the accuracy with which they report their readings to their physicians is largely unknown. The authors assessed the accuracy and quality of self-reported home blood pressure values in an ambulatory managed care population. Forty-eight hypertensive outpatients were randomly allocated to either receive information about the storage capabilities of a home blood pressure measuring device or not to receive such information. All patients were asked to record the measurement results in a logbook twice daily over a 7-day period. The main outcome measure was the difference in the number of fictional or manipulated reports per group and the difference in missing values. The combined parameter manipulated or fictional registrations occurred significantly less frequently in the informed group than in the noninformed group. (10/728 vs. 29/616; relative risk, 0.292; 95% confidence interval, 0.15-0.57; Pearson chi squared=13.15; p<0.0001). Informed patients had fewer missing registrations than the noninformed (13/728 vs. 41/616 measurements; relative risk, 0.27; 95% confidence interval, 0.15-0.47; Pearson chi squared =20.5; p<0.0001). The mean of the fictional data did not differ systematically from the mean of the correctly reported individual blood pressure values. There was no trend to over- or underestimate blood pressure values in the noninformed group. With this study design, it was possible to identify manipulation of home blood pressure values for the first time. Accuracy and interpretation of home blood pressure measurement may be increased by using devices with a memory function.

Aged↗

PubMedDate not supplied

Model-based versus clinical prediction of the spirometric response to lung volume reduction surgery.

BACKGROUND: Lung volume reduction surgery (LVRS) improves symptoms and lung function in selected patients with severe emphysema. OBJECTIVES: We investigated whether models based on physiologic and radiologic predictors discriminated patients with a favorable from those with a poor spirometric response to LVRS. METHODS: Data of a derivation cohort of 70 patients who had previously undergone LVRS served to develop two types of prediction models, lookup functions and logistic regression equations. Presence or absence of improvement in forced expiratory volume in 1 s (FEV1) > or =300 ml and forced vital capacity (FVC) > or =500 ml represented dichotomous outcomes. The residual volume/total lung capacity ratio, CT-radiological emphysema heterogeneity scores and diffusing capacity, a marker of emphysema severity, were the predictors. Models were used to predict spirometric outcomes for a validation cohort of 60 emphysema patients referred for LVRS. Furthermore, the surgeon preoperatively estimated outcomes based on all available clinical data but blinded to model predictions. Spirometric changes within 6 months following surgery were compared to predictions. RESULTS: Median FEV1 in the validation cohort increased from 0.69 to 1.00 liters (+41%), and FVC from 2.07 to 2.78 liters (+29%; p < 0.05 for changes). Lookup functions and logistic regression equations identified patients experiencing major increases in FEV1 > or =300 ml and FVC > or =500 ml with an accuracy quantified by areas under the receiver-operating characteristic curves of 0.72 to 0.76 (all areas >0.5, p < 0.05). Predictions by the surgeon had an accuracy of 0.71 to 0.78 (p = NS vs. models). CONCLUSIONS: The accuracy of models based on three predictors was fair and similar to assessment by an experienced surgeon based on all available clinical information. Prediction models may contribute to the consistent assessment of LVRS candidates.

Humans↗

PubMedDate not supplied

Identifying diagnostic studies in MEDLINE: reducing the number needed to read.

OBJECTIVES: The search filters in PubMed have become a cornerstone in information retrieval in evidence-based practice. However, the filter for diagnostic studies is not fully satisfactory, because sensitive searches have low precision. The objective of this study was to construct and validate better search strategies to identify diagnostic articles recorded on MEDLINE with special emphasis on precision. DESIGN: A comparative, retrospective analysis was conducted. Four medical journals were hand-searched for diagnostic studies published in 1989 and 1994. Four other journals were hand-searched for 1999. The three sets of studies identified were used as gold standards. A new search strategy was constructed and tested using the 1989-subset of studies and validated in both the 1994 and 1999 subsets. We identified candidate text words for search strategies using a word frequency analysis of the abstracts. According to the frequency of identified terms, searches were run for each term independently. The sensitivity, precision, and number needed to read (1/precision) of every candidate term were calculated. Terms with the highest sensitivity x precision product were used as free text terms in combination with the MeSH term "SENSITIVITY AND SPECIFICITY" using the Boolean operator OR. In the 1994 and 1999 subsets, we performed head-to-head comparisons of the currently available PubMed filter with the one we developed. MEASUREMENTS: The sensitivity, precision and the number needed to read (1/precision) were measured for different search filters. RESULTS: The most frequently occurring three truncated terms (diagnos*; predict* and accura*) in combination with the MeSH term "SENSITIVITY AND SPECIFICITY" produced a sensitivity of 98.1 percent (95% confidence interval: 89.9-99.9%) and a number needed to read of 8.3 (95% confidence interval: 6.7-11.3%). In direct comparisons of the new filter with the currently available one in PubMed using the 1994 and 1999 subsets, the new filter achieved better precision (12.0% versus 8.2% in 1994 and 5.0% versus 4.3% in 1999. The 95% confidence intervals for the differences range from 0.05% to 7.5% (p = 0.041) and -1.0% to 2.3% (p = 0.45), respectively). The new filter achieved slightly better sensitivities than the currently available one in both subsets, namely 98.1 and 96.1% (p = 0.32) versus 95.1 and 88.8% (p = 0.125). CONCLUSIONS: The quoted performance of the currently available filter for diagnostic studies in PubMed may be overstated. It appears that even single external validation may lead to over optimistic views of a filter's performance. Precision appears to be more unstable than sensitivity. In terms of sensitivity, our filter for diagnostic studies performed slightly better than the currently available one and it performed better with regards to precision in the 1994 subset. Additional research is required to determine whether these improvements are beneficial to searches in practice.

Diagnosis↗